Selective signal-responsive circuit





1. AN ELECTRICAL CIRCUIT FOR RESPONDING TO A SIGNAL OF A PREDETERMINED FREQUENCY HAVING AT LEAST A PREDETERMINED AMPLITUDE FOR AT LEAST A PREDETERMINED PERIOD OF TIME, SAID CIRCUIT COMPRISING, IN COMBINATION: AN AMPLITUDE LIMITING CIRCUIT FOR RECEIVING AN INCOMING SIGNAL; A FREQUENCY SELECTION CIRCUIT COUPLED TO THE OUTPUT OF SAID AMPLITUDE LIMITING CIRCUIT; A PEAK DETECTOR CIRCUIT COUPLED TO THE OUTPUT OF SAID FREQUENCY SELECTION CIRCUIT, AND OPERABLE FOR AMPLIFYING ONLY SUCH PORTION OF EACH CYCLE OF THE SIGNAL AS EXCEEDS A PREDETERMINED REFERENCE AMPLITUDE LEVEL: AN INTEGRATOR COUPLED TO THE OUTPUT OF SAID PEAK DETECTOR CIRCUIT; 